1. Field of the Invention
The present invention relates to a data structure of a route guidance database utilized by a route guidance device to display guiding lines for guiding a moving body as an object of route guidance on a route.
2. Description of the Related Art
A route guidance device, such as a car navigation system, utilizes two-dimensional road network data, which specifies roads by nodes and links, to search a route from a starting point to a destination specified by the user. The route guidance device displays a current location detected by, for example, GPS (global positioning system) and the searched route on a map and performs a route guidance.
Diverse techniques, for example, a computer graphics-based technique of utilizing a three-dimensional model of buildings and other features to display a map in three-dimensional representation, have recently been proposed, with a view to facilitating the user's understanding of the route guidance.
One proposed structure of the route guidance device gives a preview guidance display of a three-dimensional moving image prior, to approach to a specific traffic intersection with a higher difficulty level than a preset reference value on a route to be guided (Japanese Patent Publication No. 3,745,235). The view approach of the three-dimensional moving image is changed according to the distance from a current location to the traffic intersection.
A road network is generally constructed in the form of a two-dimensional database. When a route and a current location obtained by referring to this two-dimensional database are shown on a three-dimensionally displayed map, the route or the current location may be displayed in the air above the ground or may be displayed in the ground according to the height of the road surface. In order to solve such problems, one proposed technique utilizes a road network including height information and displays the route and the current location by taking into account the height of each point (Japanese Patent Laid-Open No. 2005-321370).
For the easy understanding of the passage behavior through a traffic intersection, one proposed technique expresses each road having an up lane and a down lane by two-dimensional links with opposite directions and provides links corresponding to a right turn and a left turn in the traffic intersection (FIG. 12, Japanese Patent Publication No. 2,866,358).
Another proposed technique using such links with directions makes the shape of a traffic intersection in a guidance display close to the actual shape (Japanese Patent Laid-Open No. 1999-108679). The technique of this cited reference provides links corresponding to a right turn and a left turn in the traffic intersection as inner-intersection links, separately from ordinary links representing ordinary road sections and recognizes multiple nodes interconnected by the inner-intersection links as one traffic intersection. The resulting display of the traffic intersection has a relatively similar shape to the actual shape of the traffic intersection.